Stuttering is a fluency disorder experienced by an estimated one percent of the total population of the United States. Two of the chief symptoms of this disorder are the repeating of speech sounds and an inability to continue speaking (commonly referred to as "blocking"). There are many more symptoms of this disorder, sharing the characteristic of preventing the stutterer from producing fluent speech, as judged subjectively by the stutterer or other listeners.
Some studies directed toward reducing stuttering have shown that stuttering can be reduced by using auditory feedback. The term "auditory feedback" is used herein to refer to providing the speaker (i.e., the stutterer) with his or her own speech while the speaker is speaking. Thus, the speaker listens to himself or herself while speaking. One of these studies, for example, has shown that introducing a short delay (i.e., of about fifty milliseconds) in the auditory feedback will significantly reduce stuttering with little or no debilitating effects on the speaker's speech rate. In other studies, altering the spectrum of the auditory feedback or introducing strong masking noise also significantly reduces stuttering. However, once the auditory feedback is discontinued, the stutter-reducing effect disappears.
These results suggest a general negative feedback model of the speech motor control system (SMCS) in the speaker's brain. FIG. 1 is a simplified block diagram of a model 10 illustrative of a generalized control system for modeling speech production. Model 10 includes a SMCS 12 and a vocal tract 14. SMCS 12 receives a target sound T that the speaker wants to enunciate and generates speech muscular control signals u(t) to control the vocal tract articulators of VT 14. In response to speech control signals u(t), VT 14 produces audio speech sounds y(t) as indicated on audio path 16. SMCS 12 then receives auditory feedback signals as indicated along path 18. In general, the feedback along path 18 can be any form of feedback and is not limited to negative feedback.
Although these auditory feedback methods do provide relief for stutters, these methods generally do not represent a treatment or cure for stuttering. In addition, the stutterer generally must use the auditory feedback equipment whenever the stutterer wishes to speak without stuttering. Of course, many stutters would find carrying such equipment with them throughout the course of a day undesirably conspicuous and inconvenient. In addition, such equipment would be subject to occasional equipment failures and to exhaustion of the power storage devices (e.g., batteries) used to power the equipment. As can be imagined, such equipment problems would generally be extremely undesirable to the stutterer if such an event unexpectedly occurred while the stutterer was trying to speak. Furthermore, with extended use, other studies suggest that any particular form of altered feedback gradually looses its effect in preventing stuttering. Accordingly, there is a need for a method or system to reduce stuttering that avoids the requirement that the stutterer carry equipment, which tends to be subject to the undesirable attributes described above.